(1) Field of the Invention
This invention relates to projection welders, and more particularly it is concerned with a projection welder suitable for use in welding nuts to a panel formed with no openings in preparation for welding the nuts to the panel.
(2) Description of the Prior Art
One type of projection welder for welding nuts on to a panel known in the art is disclosed in Japanese Utility Model Unexamined Publication No. 6580/81. This projection welder comprises maganetically attracting means located on an upper electrode for attracting a nut to the upper electrode which is moved downwardly, together with a nut, to a predetermined position on a panel located in a lower electrode, to thereby effect positioning of the nut and welding of the nut to the panel at the same time.
This projection welder of the prior art has suffered the disadvantage that variations tend to occur in the location at which the nut adheres to the upper electrode by magnetic attraction, thereby making it impossible to achieve correct positioning of the nut with the panel on the lower electrode. Thus the problem encountered is how to improve the accuracy with which the nut is positioned when it is welded to the panel. This problem could be obviated by providing the electrode to which the nut is attracted with guide means for positioning the nut. However, the provision of the guide means would create another problem. That is, when welding is performed, a shunting current might flow through the guide means when a welding current is applied, causing a lowering in the quality of the weld to occur.